This invention relates to temperature maintaining apparatuses such as transit vehicle heaters and temperature control apparatuses and methods therefor.
Various temperature maintaining apparatuses, particularly heaters, operate in a cyclic fashion. When the temperature reaches a certain threshold, such apparatuses operate for a period of time until the temperature is brought to a certain level and thereafter the apparatus becomes nonoperational until the threshold is reached again. For example, in a heater the temperature may be the temperature of a fluid and the heater operates when the temperature of the fluid drops to a set lower value. The heater continues to operate until the temperature is raised to a higher level at which time the heater switches off until the temperature again drops to the lower level.
One specific type of heater is a transit vehicle heater which operates to heat the engine coolant. The temperature of the coolant is sensed by at least one temperature sensor and the heater, typically operating on diesel fuel, is fired until the temperature of the coolant is raised to a higher level. At this point the heater switches off.
This cycling on and off between preset lower and higher temperatures produces less than satisfactory performance under some conditions. People in a transit vehicle, for example, may perceive that the temperature of the air in the vehicle drops to an uncomfortable level when the heater cycles on and off between preset lower and upper temperatures. This is because too much time may occur near the bottom of the cycle when the temperature is low and/or because the mean temperature is reduced below optimum levels. Standard on/off temperature controls or thermostats are not capable of adjusting themselves to such a situation.
Transit vehicle heaters, as well as some other types of heaters for liquids, conventionally employ two different temperature sensors. One of the sensors contacts the liquid, typically a water/anti-freeze mixture in the case of a transit vehicle heater, to determine the temperature of the liquid in order to cycle the heater on and off as required to maintain the temperature of the liquid. A second sensor contacts the inner wall of the jacket to sense an overheat condition. The need for two different sensors increases the cost and complexity of the units.
Transit vehicle heaters, and other types of heaters often must be installed in different configurations. For example, in the case of transit vehicle heaters, the direction of flow of liquid through the heaters sometimes must be reversed according to the plumbing requirements of a particular vehicle. Conventional transit vehicle heaters do not readily adapt to a reversal of liquid flow because of temperature sensors placed adjacent the fluid inlet and fluid outlet. The heater controls are adversely affected when the fluid flow is reversed because of the effect this has on the readings of the sensors.
Also some conventional heaters require two sensors adjacent the fluid inlet and fluid output respectively and cannot operate with a single sensor or with one of the sensors disabled. The controls have a lack of flexibility in this respect.
It is an object of the invention to provide an improved heat transfer device, such as a transit vehicle heater, as well as controls therefor and a method of maintaining a temperature, which are capable of adapting to different temperature conditions to maintain a more constant mean temperature compared to a simple system where the device cycles on and off at fixed temperatures.
It is another object of the invention to provide an improved heater for liquids, a method of controlling temperatures for liquids and a temperature control apparatus where a single sensor can act both to measure temperatures of the liquids to determine when the heater cycles on and off, and also acts as an overheat sensor for the heater.
It is a further object of the invention to provide an improved heater for liquids, a method of controlling such heaters and control systems for such heaters which are adaptable to varying installation requirements, such as reversing the flow of liquids through the heaters.
It is still further object of the invention to provide an improved heater for liquids, a method of controlling such heaters and a control systems for such heaters which can operate with two temperature sensors, with one of the sensors removed or with one of the sensors disabled.
There is provided, according to a first aspect of the invention, a method of maintaining a temperature between a first temperature value and a second, variable temperature value, the method utilizing a heat transfer device capable of cycling through a series of cycles. The device is capable of changing the temperature from the second value to the first value when operational. During each said cycle the device transfers heat for a first period of time when the temperature reaches the second value until the first value is reached and thereafter the device ceases to transfer heat. The first period of time is compared to a desired cycle-on period of time during each said cycle and said second value then is adjusted for a subsequent cycle of the device so said first period of time when the device transfers heat approaches said desired cycle-on period of time.
There is provided, according to a second aspect of the invention, an apparatus for maintaining a temperature between a first temperature value and a second temperature value. The apparatus includes a heat transfer device capable of cycling through a series of cycles. The device is capable of changing the temperature from the second value to the first value when operational. There are controls which control the device so during each said cycle the device transfers heat for a first period of time when the temperature reaches the second temperature value until the first value is reached and thereafter the device ceases transferring heat. The controls compare the first period of time to a desired cycle-on period of time during each said cycle and said controls adjust the second temperature value for a subsequent cycle of the device so said first period of time when the device transfers heat approaches said desired cycle-on period of time.
There is provided, according to a third aspect of the invention, a heater for a liquid including controls for maintaining a temperature of the liquid between a first value and a second lower value, the heater being capable of cycling through a series of cycles. The controls control the heater so during each said cycle the heater heats for a first period of time when the liquid cools to the second temperature value until the liquid is heated to the first value and thereafter the heater stops heating. The controls compare the first period of time to a desired cycle-on period of time during each said cycle and said controls adjust the second temperature value for a subsequent cycle of the device so said first period of time when the heater heats approaches said desired cycle-on period of time.
There is provided, according to a fourth aspect of the invention, a control system for a heat transfer device, the control system maintaining a temperature between a first value and a variable second value. The heat transfer device is capable of cycling through a series of cycles. The device is capable of changing the temperature from the second value to the first value. The control system controls the device so during each said cycle the device transfers heat for a first period of time when the temperature reaches the second temperature value until the first value is reached and thereafter the device stops transferring heat. The controls compare the first period of time to a desired cycle-on period of time during each said cycle and said control system adjusts the second temperature value for a subsequent cycle of the device so said first period of time when the device transfers heat approaches said desired cycle-on period of time.
There is provided, according to a fifth aspect of the invention, temperature controls for a liquid heater having a jacket containing the liquid. The jacket has an inner heated wall and an outer wall spaced apart from the inner wall. The controls include a temperature sensor capable of fitting to the jacket so that the sensor contacts the inner wall and the liquid. A control module monitors temperature sensed by the temperature sensor. The control module causes the heater to become nonoperational when the temperature is heated by the heater to a first value and causes the heater to operate when the liquid cools to a second value lower than the first value. The control module senses overheating when temperature sensed by the sensor increases to a third value, higher than the first value, when the heater is nonoperational, and then causes the heater to shut down.
There is provided, according to a sixth aspect of the invention, a heater for a liquid, the heater having a jacket containing the liquid. The jacket has an inner heated wall and an outer wall spaced apart from the inner wall. Temperature controls are operatively connected thereto, the controls including a temperature sensor capable of fitting to the jacket so that the sensor contacts the inner wall and the liquid, and a control module which monitors temperature sensed by the temperature sensor. The control module causes the heater to stop heating when the temperature is heated by the heater to a first temperature value and causes the heater to heat when the liquid cools to a second temperature value. The control module senses overheating when a temperature sensed by the sensor increases to a third temperature value, higher than the first temperature value, when the heater is not heating, and then causes the heater to shut down.
There is provided, according to a seventh aspect of the invention, a method of controlling temperature for a liquid heater having a jacket containing the liquid. The jacket has an inner heated wall and an outer wall spaced apart from the inner wall. The method includes fitting a temperature sensor to the jacket so that the sensor contacts the inner wall and the liquid, monitoring temperature sensed by the temperature sensor, causing the heater to stop heating when the temperature is heated by the heater to a first temperature value and causing the heater to heat when the liquid cools to a second temperature value lower than the first value, detecting when temperature sensed by the sensor increases to a third value, higher than the first value, when the heater is not heating, treating said third value as an overheat condition and then causing the heater to shut down.
There is provided, according to an eighth aspect of the invention, a temperature control apparatus for a liquid heater having two fittings for connecting liquid conduits to the heater, one of the fittings being either an inlet or an outlet for liquid, another of the fittings being another of the inlet or the outlet for the liquid. The heater has a first temperature sensor adjacent to said one fitting and a second temperature sensor adjacent to said another fitting. The apparatus includes a memory having values for a first temperature value, where the heater stops heating, a second temperature value where the heater commences heating, and a third temperature value, higher than the first value, where the heater is shut off. Both sensors are capable of sensing the first temperature value and the second temperature value and one of the sensors also senses the third temperature value. Controls compare temperature readings from each of the sensors with each of the first temperature value, the second temperature value and the third temperature value. The heater has an overheat condition when a temperature exceeds the third temperature value, a high condition when a temperature exceeds the first temperature value, a normal condition when a temperature is between the second temperature value and the first temperature value and a low condition when a temperature is less than the second temperature value. The apparatus indicates the overheat condition when one of the sensors indicates a temperature exceeding the third temperature value, the high condition when either sensor indicates a temperature exceeding the first temperature value, but neither sensor indicates a temperature exceeding the third temperature value, the normal condition when either sensor indicates a temperature exceeding the second temperature value, but neither sensor indicates a temperature exceeding the third temperature value, and a low condition when both sensors indicate temperatures less than the second temperature value.
There is provided, according to a ninth aspect of the invention, a method of controlling temperatures in a liquid heater having two fittings for connecting liquid conduits to the heater, one of the fittings being either an inlet or an outlet for liquid, another of the fittings being another of the inlet or the outlet for the liquid. The heater has a first temperature sensor adjacent to said one fitting and a second temperature sensor adjacent to said another fitting. The method includes retaining values for a first temperature, where the heater stops heating, a second temperature where the heater commences heating, and a third temperature where the heater is shut off, both sensors being capable of sensing the first temperature value and the second temperature value and one of the sensors also sensing the third temperature value, comparing temperature readings from each of the sensors with each of the second temperature value, the first temperature value and the third temperature value. The heater has an overheat condition when a temperature exceeds the third temperature value, a high condition when a temperature exceeds the first temperature value, a normal condition when a temperature is between the second temperature value and the first temperature value and a low condition when a temperature is less than the second temperature value. The overheat condition is indicated when one of the sensors indicates a temperature exceeding the third temperature value, the high condition when either sensor indicates a temperature exceeding the first temperature value, but neither sensor indicates a temperature exceeding the overheat temperature, the normal condition when either sensor indicates a temperature exceeding the second temperature value, but neither sensor indicates a temperature exceeding the first temperature value, and a low condition when both sensors indicate temperatures less than the second temperature value.
There is provided, according to a tenth aspect of the invention, a temperature control apparatus for a liquid heater having a first temperature sensor and a second temperature sensor, the apparatus including a memory having values for a first temperature, where the heater stops heating, a second temperature where the heater commences heating, and a third temperature where the heater is shut off, and controls which compare temperature readings from each of the sensors with each of the first temperature value, the second temperature value and the third temperature value. Both sensors are capable of sensing the first temperature value and the second temperature value and one of the sensors also senses the third temperature value. The heater has an overheat condition when a temperature exceeds the third temperature value, a high condition when a temperature exceeds the first temperature value, a normal condition when a temperature is between the first temperature value and the second temperature value and a low condition when a temperature is less than the second temperature value. The apparatus indicates the overheat condition when one of the sensors indicates a temperature exceeding the third temperature value, the high condition when either sensor indicates a temperature exceeding the first temperature value, but neither sensor indicates a temperature exceeding the third temperature value, the normal condition when either sensor indicates a temperature exceeding the second temperature value, but neither sensor indicates a temperature exceeding the first temperature value, and a low condition when both sensors indicate temperatures less than the second temperature value.
There is provided, according to an eleventh aspect of the invention, a method of controlling temperatures in a liquid heater, the heater having a first temperature sensor and a second temperature sensor, the method including retaining values for a first temperature value, where the heater stops heating, a second temperature value where the heater commences heating, and a third temperature value where the heater is shut off. Both sensors are capable of sensing the first temperature value and the second temperature value and one of the sensors also senses the third temperature value. Temperature readings from each of the sensors are compared with each of the first temperature value, the second temperature value and the third temperature value. The heater has an overheat condition when a temperature exceeds the third temperature value, a high condition when a temperature exceeds the first temperature value, a normal condition when a temperature is between the first temperature value and the second temperature value and a low condition when a temperature is less than the second temperature value. The overheat condition is indicated when one of the sensors indicates a temperature exceeding the third temperature value, the high condition when either sensor indicates a temperature exceeding the first temperature value, but neither sensor indicates a temperature exceeding the third temperature value, the normal condition when either sensor indicates a temperature exceeding the second temperature value, but neither sensor indicates a temperature exceeding the first temperature value, and a low condition when both sensors indicate temperatures less than the second temperature value.
There is provided, according to a twelfth aspect of the invention, a method of detecting a temperature sensor error in a heater for a liquid including a temperature sensor and controls for maintaining a temperature of the liquid between a first value and a second lower value, the heater being capable of cycling through a series of cycles. The controls control the heater so during each said cycle the heater commences heating when the temperature sensor indicates that the temperature has decreased to the lower value, the controls indicating a temperature sensor error if the temperature indicated by the sensor does not increase by a specified amount within a specified time after the heater commences heating.
The invention offers significant advantages compared to the prior art, particularly prior art heaters and other heat transfer devices which control temperature by switching on and off at fixed temperature values. By comparison the invention allow such a device to adapt to changing ambient conditions. If temperatures fall, then a heating device, for example, tends to operate longer until the temperature reaches a set upper value. This lengthened period of time is sensed by the invention and the temperature where the heater becomes operational is raised. This typically causes the heater to cycle on and off at an increased frequency. The effect is to maintain the mean temperature and give an increased degree of comfort compared with a conventional system.
At the same the invention allows such heat transfer devices to adapt in other ways. For example, a prolonged period of cooling may be sensed and the heater may be turned on even though the temperature has not fallen to a value which would normally trigger operation of the heater. This again maintains a minimum mean temperature and increases the degree of comfort.
The invention also permits a single temperature sensor to replace two different temperature sensors normally used for temperature regulation and for sensing an overheat condition. This reduces the number of parts required for devices such as transit heaters and simplifies assembly.
The invention offers significant advances and increases adaptability of various heat transfer devices such as heaters and hot liquid transit heaters in particular. For example, where such a heater has two different heat sensors the system can operate without information on which sensor is which or in which direction liquid flows through the heater. Moreover, if one sensor is removed, or one becomes faulted, then the system can adapt and still operate correctly.